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Creators/Authors contains: "Musher, Lukas J."

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  1. Abstract

    We applied an integrative taxonomic framework to evaluate the systematics of the Neotropical Black-and-white Becard (Pachyramphus albogriseusSclater 1857). Combining phylogenomic (ultraconserved elements), morphological, and vocalization data, we confirmed that this species is polyphyletic; some individuals form a clade sister to P. polychopterus and should be afforded species rank as P. salviniRichmond 1899 (Slender-billed Becard), whereas the remaining subspecies of P. albogriseus (Broad-banded Becard) are sister to P. major. We found that P. salvini differs from P. albogriseus in song, color of the lores, wing-bar width, body size, and bill width. Whereas P. albogriseus occurs in montane forest in Costa Rica and Panama (ssp. ornatus) and along the eastern slope of the Andes from northern Venezuela to southern Peru (ssp. albogriseus), P. salvini is found in the lowlands from Pacific Colombia south to northwest Peru and in the Río Marañón drainage. The latter also occurs, possibly only seasonally, along the eastern slope of the Andes, where the two species’ ranges approach closely. We treat P. a. guayaquilensisZimmer 1936 as a junior synonym of P. salviniRichmond 1899, and P. a. coronatusPhelps and Phelps 1953 as a junior synonym of P. a. albogriseusSclater 1857. This study provides a striking example of a major problem for comparative biology: underestimated and mischaracterized diversity. We argue that there are likely many more cases like this awaiting discovery.

     
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  2. Abstract

    Hybrid zones are important windows into the evolutionary dynamics of populations, revealing how processes like introgression and adaptation structure population genomic variation. Importantly, they are useful for understanding speciation and how species respond to their environments. Here, we investigate two closely related sea star species,Asterias rubensandA. forbesi, distributed along rocky European and North American coastlines of the North Atlantic, and use genome‐wide molecular markers to infer the distribution of genomic variation within and between species in this group. Using genomic data and environmental niche modelling, we document hybridization occurring between northern New England and the southern Canadian Maritimes. We investigate the factors that maintain this hybrid zone, as well as the environmental variables that putatively drive selection within and between species. We find that the two species differ in their environmental niche breadth;Asterias forbesidisplays a relatively narrow environmental niche while conversely,A. rubenshas a wider niche breadth. Species distribution models accurately predict hybrids to occur within environmental niche overlap, thereby suggesting environmental selection plays an important role in the maintenance of the hybrid zone. Our results imply that the distribution of genomic variation in North Atlantic sea stars is influenced by the environment, which will be crucial to consider as the climate changes.

     
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  3. Abstract Aim

    We aim to test the biogeographic drivers of diversification and gene‐flow at the Isthmus of Panama using a species complex of suboscine birds as a case study. We specifically evaluate whether diversification in these birds is better explained by continuous parapatry or a Refuge Model of periodic isolation and gene‐flow due glacial cycling.

    Location

    The Isthmus of Panama (Neotropics).

    Taxon

    Pachyramphus aglaiaeandPachyramphus homochrous(Aves: Tityridae).

    Methods

    We develop an approach to distinguish among the two biogeographic hypotheses—parapatric ecological speciation versus climatically mediated speciation—by making explicit predictions for demographic history, niche evolution and change in geographic connectivity over time. We sequenced genome‐wide markers (ultraconserved elements) to estimate the evolutionary and demographic history of this group. We applied both phylogenomic network analyses and demographic modelling using a supervised machine learning approach. These genetic analyses were combined with a novel distribution modelling method that estimates the probability of interspecies contact as a function of climatic conditions through time.

    Results

    We found that both spatial and genetic analyses revealed concordant results. All speciation events occurred during the Pleistocene and were characterized by non‐continuous gene‐flow, supporting a scenario of climate‐mediated diversification. Spatial connectivity was highest at present, consistent with our best demographic model of secondary contact.

    Main conclusions

    This study exemplifies a mechanism by which speciation, dispersal and introgression unfold in an important region for Neotropical diversification—the Isthmus of Panama—where periods ofbothisolation and introgression probably drive diversification. Overall, our results are consistent with the Refuge Model of biotic diversification, but suggest that introgression may be a crucial yet underappreciated component of this classic paradigm.

     
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